1. Field of the Invention
The present invention relates to a cleaner for use in cleaning a material to be cleaned, and more particularly to a cleaner including a support and an elastic blade which is bonded with the support. In addition, the present invention also relates to a process cartridge and an image forming apparatus using the cleaner.
2. Discussion of the Background
Electrophotographic image forming apparatus typically include the following devices:    (1) an image bearing member (such as photoreceptors) configured to bear an electrostatic latent image;    (2) a charging device configured to charge the image bearing member;    (3) an irradiating device configured to irradiate the charged image bearing member with imagewise light to form an electrostatic latent image on the image bearing member;    (4) a developing device configured to develop the electrostatic latent image with a developer including a toner to prepare a toner image on the image bearing member;    (5) a transfer device configured to transfer the toner image onto a receiving material; and    (6) a cleaning device configured to remove toner particles remaining on the image bearing member even after the image transfer process.
The cleaning device typically includes a cleaner having a cleaning blade. Specific examples of the blade include metal blades, and blades made of an elastic material such as urethane rubbers. Metal blades have a drawback in that the portion of the metal blades contacted with an image bearing member does not deform and thereby the tip of the metal blades cannot be closely contacted with the image bearing member. Therefore, small spaces are formed between the tip of the blade and the surface of the image bearing member if the tip has a poor dimensional accuracy or the image bearing member to be cleaned has a rough surface. When there are small spaces between the tip of the blade and the surface of the image bearing member, toner particles to be removed pass through the spaces, resulting in occurrence of a bad cleaning problem. In contrast, elastic blades can be deformed along the surface of the image bearing member and therefore the elastic blades can be closely contacted with the surface even when the tip of the blade has a poor dimensional accuracy or the image bearing member to be cleaned has a rough surface. Thus, the elastic blades have better cleanability than the metal blades. Specific examples of the materials for use in the elastic blades include rubbers.
Recently, a need exists for electrophotographic image forming apparatus capable of producing high quality images. In order to produce high quality images, it is important to use a toner having a spherical form and a small particle diameter. Specifically, spherical toners which are prepared by a polymerization method have been typically used now. Such spherical toners have an advantage of having better transfer efficiency than toners which are prepared by a pulverization method and have irregular forms. However, spherical toners have a drawback in that the toner particles remaining on an image bearing member cannot be well removed, resulting in occurrence of the bad cleaning problem (i.e., occurrence of a background fouling problem in that background areas of images are soiled with toner particles).
Then conventional cleaners for use in cleaning the surface of image forming members will be explained.
A cleaning blade is typically set so as to be contacted with a rotating image bearing member while the blade counters the rotating image bearing member to scrape off toner particles remaining on the image bearing member. Since elastic materials such as urethane rubbers used for such a cleaning blade typically have a high friction coefficient against image bearing members, the cleaning blade cannot smoothly slip on the surface of the image bearing member when the elastic materials are used as they are. Therefore, problems in that the tip of the blade is drawn by the rotated image bearing members (i.e., the tip is forcibly everted in the opposite direction, this problem is hereinafter referred to as an everted blade problem) or the tip vibrates occur. However, since toner particles and fine powders added to the toners as a fluidity improving agent are present at a nip between the blades and the surface of the image bearing members, the blades can slide on the image bearing members.
Some of toner particles scraped off an image bearing member still stay at the tip of the blade because the image bearing member is rotating. Such toner particles as staying at the tip of the blade decrease the friction coefficient between the blade and the image bearing member. Therefore, the cleaning operation can be well performed without causing the everted blade problem.
In contrast, spherical toners cannot stay at the tip of a blade. Therefore, it becomes impossible to decrease the friction coefficient between the blade and an image bearing member. In this case, the surface of the image bearing member is grounded, resulting in formation of a powder of the photosensitive layer of the image bearing member. The thus formed powder aggregates and adheres to the portion of the blade contacted with the image bearing member. Therefore, toner particles can easily pass through the contact portion, resulting in occurrence of the bad cleaning problem.
FIG. 1 is a schematic view illustrating a background cleaner. A cleaner 1A includes a support plate 2A and an elastic blade 3A which are bonded to each other. The elastic blade 3A makes a pressure-contact with the surface of a photoreceptor 4A serving as an image bearing member and rotating in a direction indicated by an arrow A. The blade 3A scrapes off toner particles T remaining on the surface of the photoreceptor 4A even after a transfer process. The elastic blade 3A is made of a material, for example, a polyurethane elastomer, and the support plate 2A is made of, for example, a metal. In this regard, a front portion of a surface 5A of the support plate 2A, which surface faces the surface of the photoreceptor 4A and which is hereinafter referred to as a first surface, is bonded with a rear portion 7A of a surface 6A of the blade 3A, which surface is hereinafter referred to as a back surface of the blade 3A (the back surface is sometimes referred to as a second surface). A front portion 8A of the elastic blade 3A extends from a tip surface 9A of the support plate 2A to the side of the photoreceptor 4A without being bonded with the support plate 2A.
In this regard, the blade 3A is pressed toward the surface of the photoreceptor 4A, and therefore the blade 3A receives a reactive force N from the photoreceptor 4A. Therefore, the elastic blade 3A is deformed so as to be curved as illustrated in FIG. 2 with exaggeration. Specifically, the blade 3A is sharply bent at a boundary portion 10A between a rear portion 7A and the front portion 8A as illustrated in FIG. 2. Therefore, the entire of the first portion of a front surface 11A of the blade 3A is contacted with the surface of the photoreceptor 4A at a contact area of AR. Namely, the body of the blade 3A contacts the surface of the photoreceptor 4A. In this case, the pressure of the blade 3A applied to the surface of the photoreceptor 4A is low, and thereby the cleanability of the blade 3A deteriorates. Particularly, in a case of a spherical toner having a high circularity, the spherical toner is rotated when the toner is contacted with the blade 3A, and thereby the toner invades the nip between the blade 3A and the surface of the photoreceptor 4A while rotating. Finally, such toner particles pass through the nip, and thereby the background fouling problem occurs. Namely, the cleaner 1A has poor cleanability.
In attempting to solve the problem, a cleaner 1B illustrated in FIG. 3 is proposed in published unexamined Japanese patent application No. (hereinafter referred to as JP-A) 2000-147970. The cleaner 1B also has an elastic blade 3B and a support plate 2B. The blade 3B has a groove 12B into which the support plate 2B is inserted. The entire surface of the groove 12B is bonded with the support plate 2B. In this cleaner, the elastic blade 3B receives a reactive force N from a photoreceptor 4B, and therefore the blade 3B tends to be bent in a direction indicated by an arrow M. However, the bottom surface of the groove 12B of the blade 3B is bonded with a tip surface 9B of the support plate 2B, and thereby the blade 3B is not bent so largely as in the case of the blade 3A. Namely, the area of the portion of a surface 11B of the blade 3B contacted with the surface of the photoreceptor 4A is not so large as that in the case of the blade 3A.
In this case, since a back surface 13B of the support plate 2B inserted into the groove 12B is also bonded with a surface 14B of the groove 12B, the surface 14B cannot slip in a direction indicated by an arrow B. Therefore, the blade 3B receives a force so as not to be bent. As a result, the amount of deformation of the blade 3B is small. In this case, the area of the portion of the blade 3B contacted with the photoreceptor 4B is excessively small, and therefore the pressure of the blade 3B applied to the photoreceptor 4B greatly varies in a longitudinal direction of the blade 3B (i.e., a direction perpendicular to the surface of the sheet including FIG. 3). Therefore, the cleaner 1B has poor cleanability. In particular, when the toner is a spherical toner, the cleaner has very poor cleanability.
Therefore, in order to impart good cleanability to a cleaner, it is necessary that the blade thereof is properly bent so that the tip of the blade is contacted with a material to be cleaned such as photoreceptors at a proper contact area, which results in increase of the contact pressure of the blade and uniformity the pressure of the blade in the longitudinal direction thereof.
JP-A 2001-312191 discloses an image forming apparatus which uses a spherical toner having a form factor SF-1 of from 100 to 140 and another form factor SF-2 of from 100 to 120 and a cleaner having a cleaning blade which is contacted with the surface of the image bearing member so as to counter the image bearing member relative to the rotation direction of the image bearing member. In this image forming apparatus, various conditions are controlled to prevent toner particles remaining on the image bearing member from passing through the nip between the blade and the surface of the image bearing member. Specifically, the conditions are as follows:    (1) linear pressure of blade: 20 to 60 gf/cm (i.e., 0.196 to 0.588 N/cm);    (2) hardness of blade: 50 to 80°; and    (3) repulsion elasticity: 10 to 50%.
JP-A 06-289760 discloses an image bearing apparatus having a cleaning device in which a cleaning metal blade held by a holding mechanism is contacted with the surface of an image bearing member and which has a pressing mechanism located between the tip of the blade and the holding mechanism. In this image forming apparatus, the holding mechanism presses the tip of the blade to the surface of the image bearing member and the pressing mechanism supplementarily presses the tip of the blade to the surface of the image bearing member.
However, as a result of the present inventors' study, it is found that the technique disclosed in JP-A 2001-312191 cannot sufficiently prevent residual spherical toner particles from passing through the nip because the linear pressure is less than 60 g/cm (0.588 N/cm). Therefore, the present inventors have investigated the mechanism of the bad cleaning problem as mentioned above. As a result thereof, the present inventors discover that the mechanism is the following.
FIG. 4 is a schematic view illustrating the configuration of a cleaning blade and an image bearing member (i.e., a photoreceptor). The tip of a cleaning blade 3 contacts the surface of a photoreceptor drum 4 so as to counter the photoreceptor drum 4 which rotates in a direction A. In this regard, the blade 3 contacts the surface of the photoreceptor drum 4 at an initial contact angle of θ, while the blade is deformed in an amount of (d).
The initial contact angle is defined as the angle formed by a line F (i.e., the line of the first surface of the blade 3 when the blade 3 is not contacted with the photoreceptor 4) and a line G which is a tangent line at an intersection C of the line F and the surface of the photoreceptor 4. In addition, the deformation amount (d) is defined as the distance between the line G and a line H which is parallel to the line G and includes an edge 3b of the blade 3 when the blade is not contacted with the photoreceptor.
When the cleaning blade 3 is set so as to have such a configuration as illustrated in FIG. 4, the procedure is as follows.    (1) at first, the edge 3b of the blade 3 is brought into contact with the surface of the photoreceptor 4; and    (2) then the blade 3 is moved so as to approach the surface along the normal line of the photoreceptor at the contact point without changing the posture of the blade so that the cleaner has the configuration as illustrated in FIG. 4.
The rear portion of the cleaning blade 3 is adhered to a metal plate 2 which serves as a support member and which is fixed to a casing (not shown). The blade 3 preferably has a thickness t1 of from 0.5 mm to 2.0 mm. The front portion of the blade 3 preferably has a length t4 of from 3.0 mm to 10.0 mm. Suitable materials for use in the blade 3 include elastic materials such as rubbers. More preferably, polyurethane having a hardness of from 65° to 80° and a repulsion elasticity of from 20 to 60% is used for the blade 3.
FIG. 5 is a schematic cross sectional view illustrating the tip portion of the blade 3 at a time the photoreceptor 4 is not rotated. In this case, the cleaning blade 3 is contacted with the photoreceptor 4 while deformed in an amount of (d). This state is hereinafter referred to as a slip state.
FIG. 6 is a schematic cross sectional view illustrating the tip portion of the blade when the photoreceptor 4 is rotated in a direction A. In this case, the edge 3b of the cleaning blade 3 is allowed to move in the direction A due to friction force between the blade and the surface of the photoreceptor, and finally a portion of the tip surface of the blade contacts the surface of the photoreceptor 4. This state is hereinafter referred to as a stick state. Numeral 3a represents a first surface of the tip portion of the blade 3.
In this case (i.e., when the photoreceptor 4 is rotated), the restoring force of the deformed portion of the blade 3 is balanced with the dynamic friction between the blade 3 and the photoreceptor 4. In contrast, when the photoreceptor is stopped, the tip portion of the blade is maintained to be deformed due to the static friction between the blade 3 and the photoreceptor 4 which is greater than the restoring force of the deformed portion of the blade 3. Therefore, when the dynamic friction does not vary and in addition the static friction is greater than the restoring force of the deformed tip portion of the blade, the stick state is maintained.
In the stick state, the area of the portion of the blade 3 contacted with the surface of the photoreceptor drum 4 is smaller than that in the slip state. In addition, in the stick state, the edge portion of the tip of blade is deformed as illustrated in FIG. 6 due to the friction force received from the photoreceptor 4. This deformation is not caused when the blade is in a slip state. The restoring force acts in such a direction that the pressure of the blade 3 to the photoreceptor 4 increases. Thus, in the stick state, the area of the portion of the blade contacted with the photoreceptor is small and in addition the compressive elasticity of the blade acts such that the pressure of the blade to the photoreceptor increases. Therefore, the pressure in the stick state is greater than that in the slip state, and thereby the toner passing problem hardly occurs. Therefore, it is preferable to stably maintain the stick state during the cleaning operation.
The present inventors made an experiment in which a cleaning blade is contacted with a surface of a transparent cylinder having the same frictional property as that of a photoreceptor drum to carefully observe the contact portion of the blade and the cylinder. Specifically, the contact portion of the blade and the transparent cylinder on which toner particles are present was observed with a camera set inside the transparent cylinder while the cylinder was rotated to determine how toner particles pass through the nip therebetween. As a result of the experiment, it was found that toner particles pass through some portions of the contact portion in the longitudinal direction of the blade, and at the portions the blade makes a stick-slip movement. The stick-slip movement means that when the position of the edge 3b of the blade 3 in the stick state as illustrated in FIG. 6 is 0 (i.e., an original point), the edge 3b moves to a point in a range of from +8 μm to +15 μm in an upstream region relative to the rotation direction of the cylinder.
As a result of the experiment and other experiments, it was found that the blade starts to make a stick-slip movement just after one or several spherical toner particles pass through a portion of the contact portion.
FIG. 7 is a schematic view illustrating the contact portion of the blade 3 and the surface of the photoreceptor 4 through which spherical toner particles are passing through. In FIG. 7, toner particles fed by the rotation of the photoreceptor drum 4 are stopped once at the contact portion of the blade 3 and the photoreceptor 4. Then the toner particles stopped by the blade 3 starts to rotate. In this case, the driving force of the rotation of the toner particles is a friction force caused by the rotation of the photoreceptor 4. Then the rotated toner particles invade into the nip between the blade 3 and the photoreceptor 4. The toner particles move through the nip while rotating in a direction indicated by an arrow and deforming the blade 3. Thus, the toner particles pass through the blade 3.
As mentioned above, the edge of the blade 3 is elastically deformed in a stick state as illustrated in FIG. 6. When spherical toner particles pass through the blade in this state, the reactive force of the photoreceptor 4, which has acted against the restoring force of the blade due to deformation of the blade, does not act on the blade. Therefore, the edge 3b of the blade 3 moves in the upstream direction relative to the rotation direction of the photoreceptor 4 due to the restoring force and has the shape of the blade in the stick state. As a result thereof, the portion of the blade has a slip state. The portion is illustrated as 3b′ surrounded by a dotted line I in FIG. 8. The portions adjacent to the portion 3b′ maintain the stick state as illustrated in FIG. 8. Therefore, the force to be applied to the portion 3b′ is diffused to the adjacent portions. As a result, a sufficient pressure does not act on the portion 3b′ achieving the slip state. Therefore, toner particles continuously pass through the portion 3b′. The edge portion of the portion 3b′ having the slip state is moved in the downstream direction to achieve again the stick state. However, the edge of portion 3b′ starts to move again in the upstream direction in the midway between the slip state position and the stick state position due to the toner particles passing through the nip, i.e., due to the restoring force of the blade. Therefore, the portion 3b′ repeats the stick-slip movement until there is no toner particle passing through the portion 3b′ of the blade. Thus, many toner particles pass through such a portion at a time, resulting in occurrence of the bad cleaning problem, i.e., occurrence of the background fouling problem in that background area of images is soiled with toner particles.
In addition, as a result of the present inventors' experiments, it was found that even when the blade does not make the stick-slip movement, the bad cleaning problem can be caused although depending on the material used for the blade.
Specifically, the toner particles stopped once by the blade 3 starts to rotate and pushes a portion of the blade 3 while deforming the portion of the blade. Finally the toner particles pass through the portion of the blade. Just after the toner particles pass through the portion, occurrence of the stick-slip movement can be prevented if the blade has low repulsion elasticity. However, even in this case, the bad cleaning problem is caused when the blade has a high hardness. Although the mechanism will be explained below in detail, the summary of the mechanism is as follows.
When the blade has a low hardness and a low repulsion elasticity, the portion of the blade deformed by toner particles passing therethrough is greatly deformed and in addition the restoring speed is slow. Therefore, when the deformed portion is restored, other toner particles pass through the portion. Therefore, the restoring action is obstructed by the following toner particles. Thus, many toner particles continuously pass through the portion, resulting in occurrence of the bad cleaning problem.
In this regard, the higher contact pressure a blade has, the better toner particle removing effect the blade has. Therefore, if the contact pressure can be set to be very high, the toner passing problem can be perfectly avoided. However, when the contact pressure is too high, the load on the image bearing member seriously increases, and thereby it becomes difficult to stably rotate the image bearing member. In addition, a problem in that the surface of the image bearing member is seriously abraded, resulting in shortening of the life of the image bearing member. Therefore, there is an upper limit of the contact pressure.
Thus, it is difficult to perfectly prevent the toner passing problem at the present time.
In addition, the stick-slip movement is also caused when the friction coefficient of an image bearing member changes and as a result the friction force formed between the blade and the surface of the image bearing member changes. Specifically, when the friction coefficient decreases, the restoring force of the blade becomes larger than the friction force formed between the blade and the surface of the image bearing member, and thereby the blade achieves the slip state. When the blade achieves the slip state, the restoring force becomes smaller than the friction force and thereby the blade is returned to the stick state due to the rotation of the image bearing member.
In contrast, when the friction coefficient of a portion of the image bearing member is relatively large compared to that of other portions, the friction force becomes larger than the restoring force of the deformed blade, and thereby the edge portion of the blade is further drawn by the image bearing member in the direction A illustrated in FIG. 6. When the portion having a large friction coefficient passes the blade, the restoring force of the blade becomes larger than the friction force, and thereby the blade achieves the slip state. When the blade achieves the slip state, the friction force becomes larger than the restoring force of the blade, and thereby the blade achieves the stick state due to rotation of the image bearing member. In this case, when the blade has the slip state, many toner particles pass through the nip between the cleaning blade and the image bearing member.
When toner particles prepared by a pulverization method are used, the toner particles stay at the contact portion of the blade and the image bearing member, and thereby the friction force formed between the edge 3b of the blade 3 and the surface of the image bearing member 4 is decreased. Therefore, the edge of the blade and the surface of the image bearing member can stably form a nip with hardly causing the stick-slip movement and thereby toner particles can be well scraped. In contrast, since spherical toner particles cannot stay at the blade, the blade repeats the stick-slip movement, and thereby an unstable nip is formed, resulting in occurrence of the bad cleaning problem.
Hereinbefore, the bad cleaning problem caused by the stick-slip movement of a blade is described. However, the cause for the bad cleaning problem is not limited to the stick-slip movement. In a background cleaner illustrated in FIG. 4, a stress is concentrated to a portion 3s of the blade 3 near an edge 2b of the metal support plate 2, resulting in occurrence of buckling of the portion 3s in that the blade 3 is sharply bent at the portion 3s. 
In order to prevent the toner passing problem, the tip portion of the blade 3 contacting the photoreceptor drum 4 is pressed to the photoreceptor at a predetermined linear pressure. Therefore, the tip portion is curved outward (i.e., in the direction opposite to the photoreceptor 4) in an amount of (d), and thereby a bending stress is generated. The bending stress is maximized at the portion 3s. In addition, the stress applied to the blade 3 is not limited to the bending stress and includes compression stress which is applied in a direction parallel to the line F in FIG. 4. If the portion 3s cannot endure these stresses, the portion 3s is buckled. If the portion 3s is buckled, the blade 3 cannot apply the predetermined linear pressure to the photoreceptor 4, and thereby the bad cleaning problem is caused.